1. Field of the Invention
This invention relates generally to a method for estimating the normal force at a wheel of a vehicle and the vertical acceleration of the vehicle and, more particularly, to a method for estimating the normal force at a wheel of a vehicle and the vertical acceleration of the vehicle for ride and stability control purposes.
2. Description of the Related Art
Continuous efforts are being made in the field of automotive industry to develop new technologies to make vehicle driving safe and comfortable. Recent developments for vehicle ride and stability control systems (VRSCS) have assisted in improving the comfort and safety of vehicles. In general, a VRSCS is an electronic control system that uses inputs from various sensors located on the vehicle and processes the information to generate a signal required for facilitating the ride comfort and the stability control of the vehicle. The normal force at a wheel and the vertical acceleration of a vehicle are two important parameters indicating whether the condition of the vehicle is comfortable and stable or unstable. Hence, constant monitoring of these parameters is imperative.
In one existing technology, the normal force at the wheel is calculated using the sprung mass of the vehicle. The sprung mass of a vehicle is the mass of the vehicle body and all the components supported by the suspension of the vehicle. Inertial sensors, such as lateral and longitudinal accelerometers, are used for this purpose and are affixed to the body of the vehicle. However, an accurate estimation of the normal force at a wheel using inertial sensors typically requires the estimation of vehicle weight and the location of its center of gravity. Further, devices, such as accelerometers, predominantly use low frequency to measure the wheel normal force as the high frequency originating from the wheel of the vehicle is generally washed out by the suspension of the vehicle. Thus, estimation of the normal force using inertial sensors installed in the sprung mass of the vehicle is typically inaccurate and not robust enough as it does not include wheel dynamics.
In one existing technology for estimating the vertical acceleration of a vehicle, a second order derivative of filtered suspension deflection sensor signals is taken as the vertical acceleration of the vehicle. However, the calculation of the second derivative of the suspension deflection signal requires heavy filtering of the signal of the suspension deflection sensors, which results in an unacceptable delay in estimating the vertical acceleration. This delay slows down the feedback process to a VRSCS in a real time environment, thus affecting the effectiveness of the VRSCS.